Background: Pneumonia is an infection of the lung tissue caused by bacteria, viruses, fungi or other microbes. Pneumonia is a common and costly disease that causes significant morbidity and mortality among the elderly population. The oral cavity long been suspected to be a source of microorganisms that cause pneumonia. Aim: The purpose of the study was that through an examination of the scientific literature to account for the link between poor oral hygiene and pneumonia in older care recipients and to investigate whether oral care can reduce the risk for the onset of pneumonia. Method: A literature review was based on 10 quantitative research studies. Literature searches were made in the databases CINAHL, Medline and PubMed. Results: The results revealed three central and essential main categories: Oral microorganisms that cause pneumonia, risk factors for pneumonia in cases of poor oral hygiene and professional oral care reduces the risk of pneumonia. Conclusion: Research studies demonstrated that oral microorganisms in the oral cavity related to poor oral hygiene is a likely source for the onset of pneumonia. Such as dental plaque, heavy plaque, disability and old age are the apparent risk factors that cause pneumonia. It also revealed that professional oral hygiene reduces the risk of pneumonia in elderly residents in need of assistance with their ADL.